This invention relates generally to a system and method for treating a patient and in particular to a system and method for controlling a treatment to administer a precise dose to a patient. In more detail, the invention relates to an apparatus and method for performing accurate surgical procedures on a particular target region within a patient utilizing previously obtained reference data indicating the position of the target region with respect to its surrounding which may contain certain reference points.
In order to control a surgical procedure, such as radiosurgery, many different prior techniques have been used including the manual targeting of the treatment. Many of the prior techniques are not sufficiently accurate so that healthy tissue surrounding the target region is often unnecessarily irradiated and damaged or killed. Other techniques are clumsy and cannot be used for particular types of treatments. For example, one prior technique involved frame-based stereotaxy that was often used for body parts and regions that could be easily physically immobilized. For example, the frame based stereotaxy was often used to immobilize the head of the patient so that a target region in the brain, such as a brain tumor, could be irradiated by the radiosurgical beam. To do so, the patient was positioned on a treatment bed and then his/her head was immobilized by a frame that was securely attached to the person's head with some attachment means and that was also securely attached to an immovable object such as a treatment table. Thus, during the treatment, the patient was not able to move his/her head at all which permitted an accurate targeting of the treatment. The problem is that a frame-based system cannot be used for fractionated treatment in which repeated smaller does are given to the patient over some predetermined period of time, such as a couple of weeks or a month. A fractionated treatment plan is often desirable since it permits larger overall doses of treatment, such as radiation, to be applied to the target region while still permitting the healthy tissue to heal. Clearly, it is extremely difficult to leave the frame secured to the patient's head for that period of time. In addition, it is impossible to remove the frame and later reposition the frame in the exact same location for the next treatment. Thus, the frame based stereotaxy provides the desired accuracy, but cannot be used with various desirable treatment schedules.
Another typical positioning system is a frameless stereotaxy system wherein a physical frame attached to the patient is not necessary. An example of a frameless stereotaxy system is disclosed in U.S. Pat. No. 5,207,223 which is owned by the same assignee as the present invention and is incorporated herein by reference. In general, a preoperative imaging of the region surrounding the target region is completed, such as by computer tomography. Then, during the treatment, a stereo image is generated, such as by X-ray imaging. The stereo image is then correlated to the preoperative image in order to locate the target region accurately. Then, a radiation source located on a robot is automatically positioned based on the correlation between the preoperative scans and the stereo images in order to accurately treat the target region without unnecessarily damaging the healthy tissue surrounding the target region.
The current frameless stereotaxic techniques have some limitations which limit their effectiveness. First, most surgical operation rooms have limited workspace and the current stereotaxic frameless systems require a large space due to the movement of the robot supporting the surgical radiation beam and the two beam imagers. Second, the cost of having two beam generators and two imagers is very high making the treatment system very expensive. These systems also typically require some form of implanted fiducials, such as markers that are viewable using an X-ray, to track soft tissue targets. Finally, for most current frameless systems, breathing and other patient motion may interfere with the target region identification and tracking due to a degradation of the images. Thus, it is desirable to provide a frameless radiosurgery treatment system and method that overcomes the above limitations and problems and it is to this end that the present invention is directed.